(i) Field of the Invention
This invention relates to a method of selectively forming an insulation layer and, more particularly, to a method of selectively forming on a workpiece an insulation layer prepared from an insulating material containing an element involved in the material forming the workpiece.
(ii) Description of the Prior Art
An insulation layer is one of the important constituent members of a semiconductor integrated circuit device (hereinafter referred to as "IC device"). The most widely accepted process of providing an insulation layer for the IC device whose substrate is formed of, for example, silicon comprises heating the silicon substrate placed in a furnace through which oxygen gas streams are made to flow, thereby forming a silicon oxide layer on the substrate. During the oxidation process, it is necessary to raise the furnace temperature to a high level such as 800.degree. C. to 1000.degree. C. Consequently, a silicon wafer is often broken or warped while being taken into or out of the furnace. Since the recent trend is toward the enlargement of a wafer, the above-mentioned drawback will become more serious in the future.
With the MOS IC device, it is customarily practised to provide a thin oxide layer having a thickness of less than one micron in order to separate the respective elements from each other. The common process of forming such an element-isolating oxide layer is represented by the so-called local oxidation of silicon (LOCOS) process which involves the application of a silicon nitride layer as an oxidation-resistant mask (namely, a mask against oxygen diffusion). The LOCOS process necessarily involves deposition, selective etching and removal of a silicon nitride layer. In addition, a silicon oxide layer must be formed between the silicon nitride layer and silicon substrate to reduce thermal stresses occurring therebetween. If, therefore, an insulation layer-selectively depositing process can be developed which can selectively form an insulation layer and allows for the application of a silicon oxide layer as a mask against oxygen diffusion, then it will be possible to shorten the steps of manufacturing an IC device and reduce its cost.
Another problem in manufacturing the IC device is that a stepped portion appears between the wiring and other sections, particularly the insulation layer. If such a stepped portion is formed, the lithography will decrease in precision, leading to a decline in the performance of the resulting IC device, when a wiring or interconnection layer has been formed over the stepped portion. Therefore, if the process is developed which enables an insulation layer to be selectively formed for insulating the respective wiring layers without the appearance of a stepped portion between the wiring and insulation layers, then it will be possible to elevate the performance of the IC device and increase its yield.